Lothian



2 Sheets-Sheet 1.. G. T'. BEIL-BY.

AIR THERMOMETER.

(No Mgdel.)

. Patented June 23,1885.

u. PETERS. mwunmm w. Walhingtnm o. c.

2 Sheets-Sheet 2.

(No Model.)

G. T. BEILBY. AIR THERMOMETER'.

No. 320,749. Patented June 23,1885.

N. PETiflS. Pllokbliihagripher, Wahlnglull, D. C.

UNITED STATES PATENT OFFICE.

GEORGE THOMAS BEILBY, OF MIDOALDER, COUNTY OF MID-LOTHIAN,

SCOTLAND.

AIR-THERMOMETER.

SPECIFIGATION forming part of Letters Patent No. 320,749, dated June 23,1885.

Application filed June 25, 1884. (No model.)

To all whom it may concern:

Be it known that I, GEORGE THOMAS BEILBY, of Midcalder, in the county ofMid- Lothian, Scotland, Fellow of the Chemical Society and chemicalengineer, have invented Improvements in Thermometers, the followingbeing a specification of the invention.

This invention has for its object improvements in instruments forascertaining the measurements of temperature, especially at points aboveor below the range of the mercurial thermometer.

The apparatus for carrying out these improvements is represented in theaccompanying drawings, in which all the figures thereof are verticalsections.

Figure l is a view of my improved thermometer. Fig. 2 is a View of thesame on a smaller scale, in which a pressure-regulator, in the form of along range or open scale barometer, is connected thereto. Figs. 3 and 4show modifications.

In the several figures like reference-letters indicate correspondingparts, with the two exceptions in reference to Figs. 3 and 4 hereinafterreferred to.

The apparatus consists of several principal parts:

First. The bulb or expanding-vessel a, filled with dry air or othersuitable gas.

Secondly. The measuring-tube b, in which the gas to be measured is cutoff from the outer air by the piston or indicator 0, of mercury or othersuitable material.

Thirdly. The connecting-tube (l, by which the gas passes from the bulbor expandingvessel a to themeasuring-tube b, or vice versa. The cubiccapacity of this tube :1 must be inconsiderable as compared with that ofthe bulb to and measuring-tube b.

Fourthly. The jacket-space e and easing f, inclosing the same andsurrounding the measuring tube 1), and through which casing f steam ofapproximately-constant pressure is passed, or in which any othersuitable medium is contained, thus forming a jacket thereof, so that thesaid measuring-tube b and its contained gas are maintained at a constantknown temperature.

Fifthly. An automatic pressure-regulator, in one form of which, asrepresented at Fig. 2, the free end of the measuring-tube bis connectedby means of the tube 9, of small bore and of convenient length, with thetube h, (which is hereinafter called the barometertube,) placedperpendicularly and closed hermetically at its upper end. In this barometer-tube h the column 75 of mercury is provided, of sufficientheight to give the desired pressure on the gas contained in themeasuring-tube b. longer than the column 1) of mercury containedtherein, so that changes of volume occurring within the apparatus causethe said column 2' to move up or down in the tube 72. without alterationof its length, and consequently without alteration of pressure.

In place of regulating the pressure of gas contained in themeasuring-tube b by the special form of barometric apparatus representedat Fig. 2, it may be regulated by means of the instruments hereinaftermore particularly de* scribed with reference to Figs. 3 and 4 of theaccompanying drawings; or, in place of an automatic pressure-regulator,an adjustable pressure-regulator may be employed.

The action of the construction of apparatus hereinbefore described is asfollows: \Vhen the bulb or expanding-vessel a is heated, the expansionof the contained gas causes a part of the said gas to be expelledthrough the connecting-tube (1 into the measuring-tube b. The piston orindicator 0, of mercury, is driven forward or upward in the said tube b,and by suitable graduation the volume of the expelled gas is measured bythe position of the said piston or indicator 0. The cubic capacity ofthe connecting-tube (Z being comparatively small, the variations of thevolume of the gas contained in it, as influenced by changes oftemperature, may be neglected without seriously aiiecting the accuracyof the observations.

The temperature and pressure of the gas in the measuring-tube b areknown and constant. The expansion of the material of the bulb a itselfcan be calculated. It .is therefore pos sible to measure with anyrequired accuracy the expansion of the original gas in the bulb a underthe influence of any unknown tem- The barometer-tube h is much peratureby measuring the volume of the gas in the measuringtube 1).

Under the system hereinbefore described with reference to Figs. 1 and 2of the accompanying drawings, the pressure of the gas or air within theinstrument is regulated by a special form of apparatus, or is allowed tovary with the atmospheric pressure. By the instrument represented atFig. 3 an approximately-constant pressure is maintained within theinstrument when at Work by continuing the free end of the measuring-tube1; into the vessel j, of comparatively large capacity. This vessel j isclosed to the outer air. It is, like the measuring-tube b, surroundedwith the steam-jacket e and easing f, by means of which a constanttemperature is maintained. When the ratio of the capacities of themeasuringtube 12 and vessel j is known, the appropriate correction forthe slightly-varying pressure within the instrument is easily applied tothe graduation.

The instrument represented at Fig. 4 is one wherein the pressure vesselor regulator takes the form of a tube, 70, returned alongside of themeasuringtube b, with which it is connected at Z, and (as in theinstrument represented at Fig. 3) is surrounded with the steam-jacket eand easing f, by means of which a constant temperature is maintained.

By the employment of the pressure vessels or regulators j and 7c in themanner shown at Figs. 3 and 4, the instrument becomes a closethermometer, which, having been once filled with dry air or gas, is notliable to derangement from tarnishing of the inside of the tubes or ofthe mercury.

The steam inlets and outlets to the steamjackets 0 upon the severalinstruments represented on the accompanying drawings are respectivelymarked m and n.

The use of an automatic pressure-regulator such as I have hereinbeforedescribed, of various forms, obviates the necessity for baro- U metricobservation such as would be needed if the free end of themeasuring-tube b were open to the atmosphere. When, however, apressure-regulator is not used, it is advisable to have the scale of thethermometer movable, so that its zero-point may be adjusted for thepressure of the atmosphere at the time of observation.

The action of the improved apparatus hereinbefore described depends onthe comparatively uniform expansion by heat of perfect gases underuniform pressure.

Hitherto no thermometer has come into ordinary use by which temperaturesabove the boiling-pointof mercury could be accurately indicated andobserved by mere inspection of a movable indicator; but with theimproved thermometers constituting this invention temperatures up to andbeyond the softening-point of glass can be observed as easily as lowertemperatures can now be with a mercury thermometer.

Thermometers constructed according to this invention may be graduated bymeasuring the capacities of the bulbs a and of the measuring-tubes b,respectively, thereafter marking off on the latter the volume ofexpelled gas corresponding with. each temperature, using in thesecalculations the cocfficient for the expansion of the gas at constantpressure.

The expansion of the gas in the bulb a with increasing temperaturescauses a decreasing amount to be expelled per degree; therefore thedegrees as marked on the measuring-tube b diminish in length toward thehigher end of the scale.

Certain fixed points of the scale may be determined by experiment, as inthe graduation of mercurial thermometers, the graduation being completedby inter and extra polation.

To facilitate the graduation of thermometers, scales or diagrams showingthe ratios of the various parts of the scale are prepared by awell-known geometric method, to which any thermometer can be readilyreferred, and from which it can be graduated.

It is evident that the apparatus and system hereinbefore described canbe applied for the determination of low as well as of high temperatures,and it is further to be seen that the said apparatus may be modifiedbyvarious alterations of outward form and arrangement Without departingfrom the essential features of the invention.

I claim 1. A thermometer formed with a bulb or expanding-vessel, ameasuringtube, and a piston or indicator in the measuring-tube, the bulbor expanding-vessel and the measuringtube, containing dry air or othersuitable gas, and the piston or indicator dividing thedry air or othersuitable gas in the measuringtube, and cutting off the outer air fromthe dry air or other suitable gas to be measured.

2. A thermometer formed with a bulb or expanding-vessel, ameasuring-tube, a piston or indicator in the measuring-tube, and a tubeof small capacity connecting the bulb or expanding-vessel with themeasuring-tube, the bulb or expanding-vessel, the measuringtube, and thetube of small diameter containing dry air or other suitable gas, and thepiston or indicator cutting off the outer air from the dry air or othersuitable gas to be measured.

3. A thermometer formed with a bulb or expanding-vessel, ameasuring-tube, a piston or indicator in the measuring-tube, and acasing forming a steam-space around the measuring-tube above and beneaththe piston or indicator, the bulb or expanding-vessel, and themeasuring-tube containing dry air or other suitable gas, and the pistonor indicator cutting off the outer air from the dry air or othersuitable gas to be measured.

4. A thermometer formed with a bulb or expanding-vessel, ameasuringtube, a piston or indicator in the measuringtube, and anextension to the measuring-tube to provide a pressure-regulator, thebulb or expandingvessel, the measuring-tube, and the extension IIOdicator cutting off the outer gas from the gas to be measured, and thebarometer forming an automatic pressure-regulator.

In testimony whereof Ihave signed my name to this specification in thepresence of two subscribing witnesses.

GEORGE THOMAS BEILBY.

Witnesses:

ROBERT ADAM GUNN, JOHN 1\/IADDER BUDHOPE, Both of 115 St. VincentStreet, Glasgow.

